Viability decay per 30 days, as the fraction remaining, by packaging form.
Liquid (Wyeast smack-packs, and any liquid pack whose maker publishes
nothing better): 0.79, i.e. the widely used "~21 % loss per month" figure
from Mr Malty's viability model. White Labs packs decay on their own
published curve instead; see PUREPITCH_RETENTION_PER_30_DAYS.
Dry: 0.96. Manufacturers publish roughly 20 % loss per year when stored
refrigerated, which is ~4 % per month.
We apply it as continuous exponential decay instead of a straight line, so
the curve stays positive and the monthly loss compounds.
Viability decay per 30 days, as the fraction remaining, by packaging form.
We apply it as continuous exponential decay instead of a straight line, so the curve stays positive and the monthly loss compounds.